Low-pressure pyrolysis of tBu2SO:: synthesis and IR spectroscopic detection of HSOH

Sulfenic acid (HSOH, 1) has been synthesized in the gas-phase by low-pressure high-temperature (1150 degrees C) pyrolysis of di-tert-butyl sulfoxide (tBu(2)SO, 2) and characterized by means of matrix isolation and gasphase IR spectroscopy. High-level coupled-cluster (CC) calculations (CCSD(T)/cc-pVTZ and CCSD(T)/ccpVQZ) support the first identification of the gas-phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix-isolated 1 have been assigned, and its rotation al-resolved gasphase IR spectrum provides additional information on the O-H and S-H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gasphase FT-IR spectroscopy reveal that, up to 500 degrees C, 2 decomposes selectively into tert-butylsulfenic acid, (tBuSOH, 3), and 2-methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3a) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas-phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6-311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3, monitored by matrix IR spectroscopy, yields short-lived I along with 2-methylpropene, but also H2O, and most probably sulfur atoms. In addition, HSSOH (6), H-2, and S2O are found among the final pyrolysis products observed at 1150 degrees C in the gas phase owing to competing intra- and intermolecular decomposition routes of 3. The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6-311G* and second-order Moller-Plesset (MP2/6311G* and RI-MP2/QZVPP) levels of theory.